An image forming apparatus of an electrophotographic type in which a photosensitive member is electrically charged by a corona charger. Especially, a product using the corona charger which is called scorotron including a grid electrode for stabilizing a charge potential of the photosensitive member has been known.
With use of the corona charger, when a foreign matter (a toner, an external additive, an electric discharge product or the like) is deposited on the grid electrode, charging non-uniformity occurs on the photosensitive member.
On the other hand, when the corona discharge occurs, an electric discharge product (ozone, nitrogen oxide or the like) is generated. When this is deposited on the photosensitive member and the electric discharge product takes up moisture in a high-humidity environment, the electric discharge product causes image defect which is called image flow. Therefore, a constitution in which with respect to a cleaning member for cleaning a surface of the grid electrode and an opening of the corona charger, the grid electrode is cleaned and the same time the opening is shielded by moving a sheet-like shutter in a longitudinal develop of the opening is described in Japanese Laid-Open Patent Application 2012-063592.
Here, in a constitution in which both the shutter and a cleaning member for cleaning the grid electrode are provided, when the foreign matter to be dropped from the grid electrode by cleaning deposits on the shutter, there is a liability that an agglomeration of the deposited foreign matter drops on the photosensitive member by vibration or the like during movement of the shutter, and therefore the deposition of the foreign matter is not preferred. For that reason, it would be considered that the drop of the agglomeration of the foreign matter on the shutter is suppressed by providing a gap between the cleaning member for cleaning the grid electrode and a leading end of the shutter with respect to the longitudinal direction of the opening so that the foreign matter does not deposit on the shutter.
However, in the constitution in which the gap is provided between the cleaning member and the shutter leading end with respect to the longitudinal direction of the opening, when an entire area of the opening of the corona charger is intended to be shielded, upsizing of the corona charger is caused.